1. Field of the Invention
The present invention pertains to a respiratory patient interface used to deliver gas to a user. In particular, the present invention is related to a respiratory patient interface having a cushion with a pleat.
2. Description of the Related Art
Obstructive sleep apnea or OSA, obstructive sleep hypopnea, and upper airway resistance syndrome (UARS) are among a variety of known disorders characterized by episodes of complete or partial upper airway obstruction during a state of diminished consciousness, such as sleep, anesthetization, or post anesthesia. OSA, hypopnea, and UARS cause intermittent interruption of ventilation during sleep with the consequence of potentially severe oxyhemoglobin desaturation. Typically, those afflicted with OSA, hypopnea, and UARS experience repeated, frequent arousal from sleep in response to the oxygen deprivation. The arousals result in sleep fragmentation and poor sleep continuity.
Consequences of OSA, hypopnea, and UARS may include debilitating daytime sleepiness and cognitive dysfunction, systemic hypertension, cardiac dysrythmias, pulmonary artery hypertension and congestive heart failure. Other consequences may include a predisposition to myocardial infarction, angina pectoris, stroke, right ventricular dysfunction with cor pulmonale, carbon dioxide retention during wakefulness as well as during sleep, and continuous, reduced arterial oxygen tension. Moreover, the cognitive impairment resulting from OSA, hypopnea, and UARS puts those afflicted at elevated risk of accidents.
The pathogenesis of the airway obstruction that characterizes OSA, hypopnea, and UARS can include both anatomic and functional abnormalities of the upper airway that result in increased air flow resistance. Such abnormalities may include narrowing of the upper airway due to suction forces created during inspiration, the effect of gravity pulling the tongue back to appose the pharyngeal wall, and insufficient muscle tone in the upper airway dilator muscles, among others. It is also believed that excessive soft tissue in the anterior and lateral neck, as commonly observed in obese persons, can apply sufficient pressure to internal structures to narrow the upper airway and restrict air flow.
Conventional treatment of OSA, hypopnea, and UARS has included surgical intervention, such as uvalopalotopharyngoplasty, gastric surgery for obesity, mandibular advancement procedures, maxillo-facial reconstruction, and tracheostomy. However, surgery potentially involves considerable risk of post-operative morbidity and mortality. In addition, the failure rate of surgery is disturbingly high. Pharmacological therapy has also been proposed to treat OSA, hypopnea, and UARS; however, results have been generally disappointing.
More recently, continuous positive airway pressure (CPAP) or bi-level positive airway pressure applied during sleep has been used to treat OSA, hypopnea, and UARS patients. Positive pressure is applied in the upper airway to splint or support the airway open, thereby preventing its collapse and the resultant airway obstruction. A typical positive airway pressure device comprises a flow generator (e.g., a blower) that delivers gas via a delivery conduit to a patient interface, such as a mask. It is also known to deliver the positive airway pressure therapy as a continuous positive airway pressure (CPAP), a variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle (Bi-PAP), or an auto-titrating pressure that varies with the monitored condition of the patient. Pressure support therapies are also provided to treat other medical and respiratory disorders, such as Cheynes-Stokes respiration, congestive heart failure, and stroke.
Many patient interfaces are well known in the art. For instance, masks which provide a seal between the compressed air and the patient are common. These interfaces include nasal pillows with prongs which fit into the nares of the patient, nasal masks which fit over the patient's nose, nasal-oral masks that fit over the mouth and nose, and full face masks which fit over the patient's entire face. For such devices to be effective, two competing goals need to be balanced: comfort and support. Comfort may be enhanced by reducing the area of contact between the mask and the patient; or use of a soft, lightweight, flexible material. If the mask proves to be uncomfortable, patient compliance will be low. In contrast, to enhance the ability of the mask to support its weight and associated hoses and attachments, the mask should ideally be constructed from a rigid material and have a large contact area between the mask and the patient.
One mask which attempts to balance the competing goals of comfort and support is disclosed in U.S. Pat. No. 4,907,584. This mask has a rigid support portion and a cushion. The cushion includes a flexible flap to form a seal between the patient and the mask. In order for the flap to operate effectively, the flap must be sufficiently rigid to support the mask and sufficiently flexible to be comfortable. Although the '584 patent has substantially advanced the art, it could still be further improved upon. For instance, since the flap is required to balance between comfort and support, the resulting design must compromise between these two goals.
Other patient interfaces have been suggested which have separate structural features to address the competing goals of support and comfort. For instance, U.S. Patent Application Publication No. 2004/0112385 discloses a mask having a rigid support attached to a cushion. The cushion disclosed in the application includes a double flap. The outer flap contacts the face of the patient and is formed to be flexible in order to provide a comfortable seal. The inner flap is formed to provide support to the cushion either alone or in combination with the outer flap.
This device advances the art by separating the two competing goals of comfort and support into separate structural elements. By so doing, this allows each of these features to be customized to achieve their separate purpose rather than having a single structural element which attempts to balance these two competing goals. Yet, even this design presents several drawbacks. One major drawback to this design is that it assumes the forces exerted on the mask are consistent about its circumference. In reality, the region about a patient's mouth and/or nose has a complex geometry requiring differing amounts of flexibility and support to achieve an adequate seal and differing amounts of rigidity to provide adequate support. Secondly, forming a cushion with an internal flap has proved difficult to manufacture and has resulted in rejects and wasted material. Typically, these masks are manufactured by an injection molding process. One drawback to this manufacturing method is that it is difficult to flow material into thin walls and undercuts as is needed to form this type of cushion.
To overcome these disadvantages, other masks have been suggested to provide a separate structure to seal the mask and a separate structure to provide support while simplifying the manufacturing process. One such mask is disclosed in U.S. Pat. No. 5,349,949. The mask disclosed in this patent has a rigid shell provided with fastening straps to hold the mask on the user's head. Connected to the shell is a face cover constructed from an elastomeric material. The face cover contacts the user's face along an internal lip. Adjacent to the lip is a deformable fold with resilient spring-like elements. One advantage this device has over the device disclosed in the previous publication is that it removes the thin walls and undercuts while separating the structure used to provide a seal from the structure used to provide support to the face cover. Yet, even this device has several drawbacks. For instance, the deformable fold has a consistence shape about the circumference of the face cover. Therefore, it is incapable of providing differing support and flexibility as needed about the user's face.
Accordingly, it would be desirable to have a respiratory mask that is configured to deliver a gas to a patient. It would also be desirable to have a respiratory mask that provides separate structural elements to provide support and flexibility to the respiratory mask. It would be further desirable to have a respiratory mask which is capable of providing differing support and flexibility in different regions of the mask. It would still be further desirable to have a respiratory mask that is capable of providing the above noted features while being constructed in a manner that simplifies the manufacturing process.